1. Field of the Invention
The present invention relates to a pivot bearing, particular to a pivot bearing used for a disc drive memory system.
2. Description of the Related Art
As shown in FIGS. 1 and 2, a conventional pivot bearing comprises a pair of cylindrical inner rings 102 fixedly mounted on a shaft 101, a pair of cylindrical outer rings 103 coaxially surrounding the corresponding inner rings 102, a plurality of rollable balls 104 arranged between the inner rings 102 and the outer rings 103 and rotatable in the circumferential directions of the inner and outer rings 102 and 103 so that a relative rotational movement is made between the inner rings 102 and the outer rings 103 through the balls 104. The pivot bearing further has a sleeve 105 into which the outer rings 103 are fixedly inserted. The sleeve 105 is tightly inserted into a fixing hole formed in an external member such as the actuator block of a memory device.
FIG. 1 shows a conventional standard dual row type pivot bearing which has an annular spacer 106 sandwiched between the two outer rings 103. FIG. 2 shows a conventional dual row type pivot bearing, that is, an abutment dual row type pivot bearing in which the opposed ends of the two outer rings 103 are abutted against each other.
When such a pivot bearing is used for a precision machine or a precision instrument such as the actuator block of a rotary type recording medium apparatus, the bearing must be operated at very little irregular rotation and very little run-out and must be miniaturized. In order to reduce the irregular rotation and run-out, the dimensional accuracy and the assembly accuracy must be improved and it is desired that generation of out-gas (gas discharged from adhesive applied to the portions between the components of the bearing which are bonded together) be suppressed to a minimum or prevented by reducing the areas of the bonded portions or without using the adhesive. Further, it is desired that the number of the components of the pivot bearing be reduced in order to lower the number of the assembly steps and the manufacturing cost of the bearing.
It might be possible to overcome the above-mentioned disadvantages from the conventional pivot bearing by removing a sleeve from the bearing and inserting the outer rings of the bearing into a fixing hole formed in a component of a precision machine or a precision instrument. However, since the thin outer rings without being enforced are applied with a load from the external component, such a modified pivot bearing has a disadvantage that it can be used only when a low load is applied.
An object of the present invention is to provide a sleeveless pivot bearing which has such thicker outer rings than the outer rings of the conventional pivot bearing as bear load from the external member of the outer rings of the sleeveless pivot bearing, irregular rotation and run-out of the pivot bearing are prevented from occurring, the number of the assembly steps and the manufacturing cost are reduced, and adhesive which bonds the outer rings to an outer-ring holding external member and from which out-gas will be produced is not used.
Another object of the present invention is to provide a pivot bearing wherein the other components of the pivot bearing than the outer rings use commercially available components or components manufactured in the ordinary manufacturing line at ball bearing manufacturers"" factories, whereby the cost of the production facilities and the manufacturing cost are reduced.
A further object of the present invention is to provide a miniaturized pivot bearing.
In order to achieve the objects of the present invention, a pivot bearing according to the present invention comprises a shaft, at least two cylindrical inner rings arranged in tandem and fixedly mounted on the shaft, at least two cylindrical outer rings arranged in tandem and coaxially surrounding the inner rings, rolling elements disposed between the inner rings and the outer rings and arranged circumferentially of them, wherein the outer rings inserted into an external member and fixed thereto have such a thickness that the outer ring can bear load applied from the external member.
The thickness of each of the outer rings of the pivot bearing of the present invention can have substantially the same thickness as the sum of the thickness of the outer rings and the thickness of the sleeve of the conventional pivot bearing.
The outer rings can be abutted against each other at adjacent ends of adjacent ones of the outer rings. Alternatively, an annular spacer surrounding said shaft is provided between each of adjacent pairs of the outer rings.
The outer rings can be directly fixed to the external member. Alternatively, a tolerance ring can be provided so as to surround said outer rings, for fixing the outer rings to the external member at a fixing hole formed therein. The tolerance ring can be formed by winding a steel plate into a cylindrical shape.
A holding mechanism for holding the tolerance ring can be provided on or in the outer rings. The holding mechanism can comprise snap rings provided in the outside outer rings, for receiving the engaging portions of the tolerance ring formed on its both ends. Alternatively, the holding mechanism can comprise enlarged annular flange portions each provided on each of the outside outer rings.
The pivot bearing can be of a multiple outer ring type comprising more than two outer rings. Further, the pivot bearing is of a ball bearing type.